It's a looming spectre both National and Labour say could derail the election, but which party stands to lose the most from a low voter turnout at the polls?

Figures from the latest Stuff-Ipsos poll show 77 per cent of people say only unforeseen events like illness or disaster would stop them voting.

When the remainder were asked what might put them off voting, 17.6 per cent said it was too difficult to get to a polling station, while 8 per cent said they were too busy and a further 8 per cent said they didn't know enough about the issues or the candidates.

The data suggests this election could mirror 2011 when turnout sunk to 74.2 per cent - the lowest since 1981.

National Party campaign director Steven Joyce said despite many polls showing the election was National's to lose, a Labour-led government was still a realistic outcome.

"I think firstly, these are polls and the nature of polls is that they're people's opinions at a point in time and that makes it a reasonably costless sort of opinion."

Joyce said the bulk of the missing voters were likely National supporters who thought the election was a foregone conclusion.

"As we have pointed out previously, if you look at the decline in turnout in 2011, 10 of the top 12 electorates that declined were safe National seats," he said.

"That worries us, because it seems that at that stage too many people thought the result was decided and went to the beach or wherever, rather than vote."

But Labour Party campaign director Dave Talbot said National was "plain wrong", and those voters were most likely from the Left.

It would ultimately be a grassroots campaign that would mobilise them.

"To shift people who are reluctant voters you need to make personal connections. They're harder to reach via traditional media, so you have to get to them face to face," Talbot said.

The Labour campaign team had already made five times more phone calls than it had at the same point in the last campaign - surpassing the 200,000 mark.

Victoria University political science Professor Jack Vowles said the election would have to be "incredibly close" for low voter turnout to have an effect on the final vote.

It seemed Labour and the Greens, as a block, were trailing too far behind National.

"And the point to make is if there is differential turnout, if National supporters stay home and Labour voters turn out, as far as the election result is concerned, that's how the votes fall and people should have gotten out to vote.

"So I'm not sure that a very close election where one or other party, or block of parties, got the edge you could say would be a rogue election, you would just say one party got its vote out and the other one didn't and that's the way the game is played."

Vowles heads the national Election Survey, which measures voting and non-voting patterns after every general election.

Last carried out in 2012, it found younger voters, those on a lower income, and migrants were among the biggest groups of non-voters.

But said Vowles said the statistics were not always clear cut.

Although few of those demographics footed the bill of a typical National voter, there was an obvious portion of potential National voters, who did not vote last time.

Chief electoral officer Robert Peden said New Zealand had gone from a "world class" rate of civic engagement, to a "barely average" one.

"So we're not going to be able to turn this around quickly or easily.

"We need to take a long-term approach and an important aspect of that is civics education and also just encouraging a conversation among New Zealanders about why it's important," he said. The Electoral Commission has begun a "Voting in Schools" campaign, and would also be rolling out a "modest" educational ad campaign ahead of September 20.

Although most democracies throughout the world were experiencing similar declines in voter turnout, Peden said New Zealand's was particularly steep.

"Partly because we started at such a high point... but we are rapidly catching up to a point where we would not want to be so now is the time to start doing something about it."